FLOW AND HEAT TRANSFER IN A RIBBED CONVERGING-DIVERGING U-DUCT UNDER ROTATING AND NON-ROTATING CONDITIONS

A numerical study based on steady RANS with the SST turbulence model was performed to investigate the flow and heat transfer in a ribbed U-duct with a rectangular cross section that converges linearly in the radially outward direction and diverges linearly in the radially inward direction under rotating and non-rotating conditions. Parameters examined include rotation number (Ro(i) = 0, 0.0219, 0.0336, 0.0731), Reynolds number (Rei = 46,000, 100,000, and 154,000), and the duct's taper angle (a = 0 degrees and 1.41 degrees) under conditions relevant to gas turbines used for electric power generation. Results obtained show that increasing the taper angle from 0 degrees to 1.41 degrees, which appears negligibly small, significantly increases both the friction coefficient and the Nusselt number whether there is rotation or not. With rotation at Ro(i) = 0.0336 and Re-i = 100,000, the maximum increase in the average friction coefficient and Nusselt number was found to be 41.7% and 36.6% respectively. Without rotation at Re-i = 46,000, those are 11.5% and 14.7% respectively.